As gearings that can change rotary motion, it is common to use gearings employing a pulse motor, a servo motor or the like to change the rotary motion by electrical control. In such gearings, however, the motors such as the pulse motor and the servo motor themselves are expensive and also electric circuits for controlling such motors must be provided, resulting in a very high price as the whole device.
Gearings that mechanically change the rotary motion by utilizing various types of cam mechanisms are also known in the art, where, however, a high precision is required in the designing and manufacture of the cams. Moreover, interlocking mechanisms around the cams are required in order to achieve the intended movement, so that the device must be made complicated, also resulting in a high production cost.
Meanwhile, in Japanese Patent Application Laid-open No. 4-175550, the present inventor has already proposed a variable-speed rotary gearing made up of gears, one-way clutches and coiled springs. In the variable-speed rotary gearing, a variable rotary motion that periodically repeats acceleration and deceleration can be obtained through a drive shaft of a motor rotating at a constant speed.
The gearing disclosed in Japanese Patent Application Laid-open No. 4-175550, however, is a gearing that performs variable-speed rotation repeating acceleration and deceleration, and it has been impossible to perform intermittent rotary motion.